Current environmental concerns, in particular with a view to reducing CO2 emissions, lead to a reduction in the fuel consumption of light vehicles. This reduction in energy consumption can be carried out via elements such as the engine and/or the transmissions, such as the axles or the dual clutch gearboxes and in particular manual gearboxes. In order to reduce fuel consumption, it is possible to use polymers which improve the viscosity index (VI) in order to act on the viscosity of the lubricant or to use friction modifiers in order to act on the coefficient of friction of the lubricant. U.S. Pat. Nos. 6,268,316, 4,707,301 and 5,439,605 describe a lubricant composition comprising an ethylene/propylene copolymer and a dimercaptothiadiazole derivative.